Allow muting/unmuting audio through media track API

media/renderers/renderer_impl.h

Index: media/renderers/renderer_impl.h
diff --git a/media/renderers/renderer_impl.h b/media/renderers/renderer_impl.h
index fc17f6cbdf628ee1534e49890275856f156e6300..6345ecf1387838359c91692aeca0e571d2ee377f 100644
--- a/media/renderers/renderer_impl.h
+++ b/media/renderers/renderer_impl.h
@@ -63,6 +63,10 @@ class MEDIA_EXPORT RendererImpl : public Renderer {
   base::TimeDelta GetMediaTime() final;
   bool HasAudio() final;
   bool HasVideo() final;
+  void OnEnabledAudioStreamsChanged(
+      const std::vector<const DemuxerStream*>& enabledAudioStreams) final;
+  void OnSelectedVideoStreamChanged(
+      const DemuxerStream* selectedVideoStream) final;
 
   // Helper functions for testing purposes. Must be called before Initialize().
   void DisableUnderflowForTesting();
@@ -151,6 +155,9 @@ class MEDIA_EXPORT RendererImpl : public Renderer {
   scoped_ptr<AudioRenderer> audio_renderer_;
   scoped_ptr<VideoRenderer> video_renderer_;
 
+  bool audio_stream_currently_disabled_ = false;
+  float audio_volume_ = 1.0f;
+
   // Renderer-provided time source used to control playback.
   TimeSource* time_source_;
   scoped_ptr<WallClockTimeSource> wall_clock_time_source_;